Salt-Enhanced Oxidative Addition of Iodobenzene to Pd: An Interplay Between Cation, Anion, and Pd-Pd Cooperative Effects br

Halide salts facilitate the oxidative addition of organichalides to Pd(0). This phenomenon originates from a combination ofanionic, cationic, and Pd-Pd cooperative effects. Exhaustive computa-tional exploration at the density functional theory level of the complexesobtained from [Pd0(PPh3)2] and a salt (NMe4Cl or LiCl) showed thatchlorides promote phosphine release, leading to a mixture ofmononuclear and dinuclear Pd(0) complexes. Anionic Pd(0) dinuclearcomplexes exhibit a cooperativity between Pd(0) centers, which favorsthe oxidative addition of iodobenzene. The higher activity of Pd(0)dimers toward oxidative addition rationalizes the previously reportedkinetic laws. In the presence of Li+, the oxidative addition to mononuclear[Pd0L(Li2Cl2)] is estimated barrierless. LiCl coordination polarizes Pd(0), enlarging both the electrophilicity and the nucleophilicityof the complex, which promotes both coordination of the substrate and the subsequent insertion into the C-I bond. Theseconclusions are paving the way to the rational use of the salt effects in catalysis for the activation of more challenging bonds.